Hitherto, inorganic photographic materials such as amorphous selenium, selenium alloys, cadmium sulfide and zinc oxide and organic photographic materials represented by polyvinylcarbazole and polyvinylcarbazole derivatives are widely known as electrophotographic photoreceptons.
It is well known that amorphous selenium or selenium alloys have superior properties as electrophotographic photoreceptors and have been put into practice use. However, in producing these materials, a complicated vacuum deposition process is necessary, and further the vacuum-deposited film obtained has a disadvantage in that the film lacks flexibility. Zinc oxide is used as a dispersed photographic material in which zinc oxide is dispersed in a resin, but such material has a problem such as a low mechanical strength and cannot be used repeatedly as is.
Polyvinylcarbazoles known as organic photoconductive materials have advantages such as transparency, good film-forming property and flexibility, but polyvinylcarbazoles per se have no photosensitivity in at visible ray region, an cannot be used practically alone. Accordingly, various sensitization methods have been proposed therefor. Although a spectral sensitization of polyvinylcarbazole using a sensitizing dye has resulted in expanded spectral sensitivities extending to visible ray region, a sufficient photographic sensitivity as electrophotographic photoreceptors cannot be obtained, and it still has a drawback that a photo-fatigue is remarkable.
On the other hand, a spectral sensitization with an electron acceptor gives rise to electrophotographic photoreceptors having a sufficient photosensitivity, and some of them has been practically used. However, there are still more problems on mechanical strength and durability.
Various extensive studies have been made on photosensitive materials and there are many reports. However, electrophotographic photoreceptors having a superior electric characteristic and a sufficient photosensitivity have not yet been obtained. At present, there are reports about phthalocyanines which show superior electrophotographic characteristics as dispersed photosensitive materials. However, their spectral sensitivity is partial to long wavelength region, and they have a drawback that reproduction of red color is inferior.